title: Flavonoid regulation of HCN2 channels.
abstract: The hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are pacemaker channels whose currents contribute to rhythmic activity in the heart and brain. HCN channels open in response to hyperpolarizing voltages, and the binding of cAMP to their cyclic nucleotide-binding domain (CNBD) facilitates channel opening. Here, we report that, like cAMP, the flavonoid fisetin potentiates HCN2 channel gating. Fisetin sped HCN2 activation and shifted the conductance-voltage relationship to more depolarizing potentials with a half-maximal effective concentration (EC50) of 1.8 μM. When applied together, fisetin and cAMP regulated HCN2 gating in a nonadditive fashion. Fisetin did not potentiate HCN2 channels lacking their CNBD, and two independent fluorescence-based binding assays reported that fisetin bound to the purified CNBD. These data suggest that the CNBD mediates the fisetin potentiation of HCN2 channels. Moreover, binding assays suggest that fisetin and cAMP partially compete for binding to the CNBD. NMR experiments demonstrated that fisetin binds within the cAMP-binding pocket, interacting with some of the same residues as cAMP. Together, these data indicate that fisetin is a partial agonist for HCN2 channels.
authors.affiliation: From the Departments of Physiology and Biophysics and.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Carlson
authors.forename: Joel C
authors.initials: JC
authors.lastname: Rosenbaum
authors.forename: Tinatin I
authors.initials: TI
authors.lastname: Brelidze
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Klevit
authors.forename: William N
authors.initials: WN
authors.lastname: Zagotta
mesh_terms: D000818:Animals; D001665:Binding Sites; D000242:Cyclic AMP / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005419:Flavonoids / Q000737:chemistry / Q000494:pharmacology*; D044948:Flavonols; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D019906:Nuclear Magnetic Resonance, Biomolecular; D015221:Potassium Channels / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D014982:Xenopus laevis
chemical_list: D005419:Flavonoids; D044948:Flavonols; C578711:Hcn2 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015221:Potassium Channels; D000242:Cyclic AMP; C017875:fisetin
keywords: Cyclic AMP (cAMP); Electrophysiology; Flavonoids; Fluorescence Anisotropy; Fluorescence Resonance Energy Transfer (FRET); HCN; Ion Channels; NMR; Purine Ring